Across
1
Mass per unit volume
4
Amplified beam of light
5
Preserved remains of ancient life
8
Gas essential for breathing
9
Push or pull on an object
10
Group of similar cells
11
Tissue that contracts for movement
12
Positive particle in nucleus
Down
2
Second lightest element
3
Substance with pH below 7
6
Center of an atom or cell
7
Path of a planet around the sun